void main(List<String> args) {
  Persion persion = new Persion("yjh");
  print(persion.age);
}

class Persion {
  String? name;
  int? age;
  // 函数的重定向
  Persion(String name) : this.init(0, name);
  Persion.init(this.age, this.name);
}
